RESUMO
Certain changes in the epidermis are important because they may, if left untreated, go on to become malignant tumours [NMSC]; namely BCC and SCC. Some, such as solar keratosis and leukoplakia of mucosal surfaces, may show little evidence of cellular unrest for much of their natural history. Others, like Bowen's disease or erythroplasia of Queyrat, may have the microscopical feature of intra-epidermal carcinoma from the beginning. Skin damaged by ionizing radiation, radiant heat or exposure to tar and other carcinogenic compounds and the keratoses that follow ingestion of inorgarsenic compounds, are also potentially malignant. Occasionally, long standing scars, sinuses and ulcers may be the site of cancer. Rarely, a burn or other injury may be followed almost immediately by a squamous cell carcinoma. The cumulative effect of UV radiation is to act directly on the epidermis and indirectly through the dermal changes. Also xerodermia pigmentosa, epidermolysis bullosa, condyloma accuminata, epidermodysplasia verruciformos, chronic discoid lupus erytheromatous and cutaneous horns may be complicated by malignant changes. The aim of the work was to identify various precancerous skin diseases in those attending outpatient clinic or admitted and treated in the inpatient clinic of dermatology department, Alexandria Faculty of Medicine [1990-1995], to quantify their relative frequencies and describe their age and sex distribution and compare and interpret the findings